Plant and soil properties determine microbial community structure of shared Pinus-Vaccinium rhizospheres in petroleum hydrocarbon contaminated forest soils

Abstract

Rhizosphere communities are critical to plant and ecosystem function, yet our understanding of the role of disturbance in structuring these communities is limited. We tested the hypothesis that soil contamination with petroleum hydrocarbons (PHCs) alters spatial patterns of ecto- (ECM) and ericoid (ERM) mycorrhizal fungal and root-associated bacterial community structure in the shared rhizosphere of pine (Pinus contorta var. latifolia) and lingonberry (Vaccinium vitis-idaea) in reconstructed sub-boreal forest soils. Pine seeds and lingonberry cuttings were planted into containers with an organic (mor humus, FH or coarse woody debris, CWD) layer overlying sandy mineral horizons (Ae and Bf) of forest soils collected from field sites in central British Columbia, Canada. After 4 months, 219 mg cm-2 crude oil was applied to the soil surface of half of the systems; systems were sampled 1 or 16 weeks later. Composition, relative abundance and vertical distribution of pine ECMs were assessed using light microscopy; community profiles were generated using LH-PCR of ribosomal DNA. Multivariate analysis revealed that plant and soil factors were more important determinants of community composition than was crude oil treatment. Fungal communities differed between pine and lingonberry roots; ECM communities were structured by soil layer whereas ERM communities varied between FH and CWD soil systems. Bacterial communities varied between plants and soil layers, indicating properties of ECM and ERM rhizospheres and the soil environment influence bacterial niche differentiation. This integration of mycorrhizal and bacterial community analysis contributes to a greater understanding of forest soil sustainability in forest ecosystems potentially contaminated with PHCs.